Method of producing titanium



j cation Serial No. 373,512, filed August 11 "1953.

. v 2,846,304 I r f METHOD on PRODUCING TITANIUM Wa ne H. Keller, Waban,and Irwin's. Zonis, Belmont,

-Mass., assignors to National Research Corporation,

Cambridge, Mass'., a corporation of Massachusetts.

' 7 No Drawing. ApplicationJune 4, 1954 Serial No. 434,648

9 Claims. (Cl. 75-845) This invention relates to-the production oftitanium and 'r'nore particularly to the production of'titanium bya-process wherein a titanium compound .is dissolved in a fused salt andis reduced to crystalline titanium-metal by the addition of a moltenreducing agent. This application is, in part, a continuation ofourcopending app-1' A principal object of the present invention is topro- 7 vide an improved process for producing high yields ofcrystallinetitanium by the reduction of a titanium chloride dissolved in a fusedsalt.

- .Another object-of the invention is to provide a proc-' ess of theabove type which is simple and cheap to operate and gives a productwhich can be water leached to separate the titanium crystals from theby-product salt. Other objects of the invention will in part and will inpart appear hereinafter.

The invention accordingly comprises the processinvolving the severalsteps and the relation and the orderi of one or more of such steps withrespect to each of the others which are exemplified in the followingdetailed disclosure, and the scope of the application of which willbeindicatedinthe claims. 7" I 9 For a fuller understanding of the'natureand-objects of-theinvention, reference should be had to the followingdetailed description. i

In the present invention, advantageis taken of-the well-known ability ofthe alkali and alkaline earth metals to reduce titanium tetrachloride,for example, to' titanium metal. This reaction proceeds rapidlyatrelatively.

low temperatures (i. e., temperatures on the order of themelting pointof'the by-product halide). However,

,7 in the present invention the reaction conditions are so adjusted thatthe product titanium consists of crystals ofptitanium which have a sizesufficiently large 'so' as to permit simple leaching with water(containing a small percentage of acid) to dissolve the by-producthalide.

The'size of the individual crystals is such that the surface-to-volumeratio is relatively low, thereby'preventing contaminationof the productdue to the presence" ofsurface oxide. The naturelof the product is alsosuch'that its surface activity appears to be very low.

In accordance with the present invention, a titanium compound to bereduced, preferably a lower halide; is

dissolved in' a fused salt and is reduced to titaniummetal' by additionof a reducing agent such as sodium, potassium, magnesium and thelike. I

We have discovered that in such a system crystal growth is strongly.promoted'if the reducing agent be supplied to the titanium halide fusedsalt solution via an interposed shielding layer of fused salt which issubstantially free of the titanium halide and which is preferablylocalized by, and at'least in part incorporated in, a solid porousdiaphragm which is in direct contact 1 with the solution.' We have alsofound that such shielding layer and porous diaphragm can beestablishedand maintained by proper controlj'of the condition ofthe be obvious:

United States Patent ice bath and of the manner of thereto. I Forexample, in a preferred practice-of the} invention, a solution oftitanium trichloride and titanium dichloride in fused sodium chloride isprovided in, a reactor and liquid sodiumiis fed to the surface. of theride at least adjacent and above the top of the crust.

As the process continues, the level of the salt bath will rise due tothe manufacture of more by -product salt but the crust remains where itwas-formed, adhered to, the Walls .of the reactor, and the titaniumcrust becomes covered by a layer of moltensalt which (due to strati:

fication and diffusion limitations placed on the contents;- of the bathdue to the presence of. thecrust) is substantially free -of titaniumchloride. Consequently, further feedof sodium is to the surface of freelayer of salt above the titanium crust. I

When thecrust and shielding layer of .ti'ta nium-halidefree salt havebeenestablished, titanium crystals begin;

to form, growing out of the under surface of the crust and outwardlyfromthe walls of the. reactor. The pros duction of titanium fines, suchas initially form the crust,

"decreases substantially. I The feed of sodium is preferably continueduntil sufficient sodium has been fed to reduce substantially all; of,the dissolved titanium/chloride to titanium metal. The sodium feedrateis also. preferably maintained-atless than about five pounds perhour per square foot of salt bath surface. This feed'rate is preferablyon the order of two pounds orlessof sodium per hour per square foot ofreactor surface at the startof the reduction of the solution of lowertitanium chlorides. Ityis also preferred-that the lower, chloridesolution be -rela-,

tively. concentrated atthe start of the reduction so as to assist informing a self-supporting, porous initial crust. After the crust andtitanium-chloride-free salt layer have been formed, the feed rate ofsodiumto the reactor can be considerably increased,'if desired. 'How-.

ever, from the standpoint of mechanical simplicity and safety, aconstant, relatively slow rate of feed of sodium is preferred. 7

After the sodium feed is stopped, the reactor is allowed 7 to cool andthe solidified contents are leached by means of acidified water,thusremoving the salt. The-remain ing product consistsessentially of amass of loosely adherent, interlaced crystals of titanium extendingdownwardly from .the crust layer -of sinter'ed-titanium particles 1 andoutwardly from the reactor walls.

It will be evident fnom the foregoing that the porous diaphragm, whichin the example just described islformed of sintered titanium fines,performs two major-functions. First, it helps to segregate the fusedsalt layer low. inf f Second, it forms a supporting stratum titaniumchloride. from which the crystals may grow.

In order to describe more fully preferred methods of practicing theinvention, there are set forth below three non-limiting exampleswhichare merely illustrative of A numerous additional embodiments of theinventio nfln these examples, the process was, carried out in a nickelreactor having a diameter of 12 inches anda height of 27 inches. Thereactor had a water-cooled head, andwas equipped .with .a stirrer foragitating the .salt bath 'inthe Patented g-L F supplying thereducingagent this titanium-chloridereactor. A feed tube was provided forfeeding liquid titanium tetrachloride below, the surface of the bath andanother feed tube was included for feeding sodium to thesurfaceof thebath. Temperatures were indicated by thermocouples positioned within thesalt charge. An atmosphere: of argon was maintained in thereactorduring' theruns.

Example I 39.5 pounds of sodium chloride were charged into'the reactor.All air was removed from the reactor and an atmosphere of argonintroduced therein. Sodium and titanium tetrachloride were introducedfor 1 hour and 11 minutes at the rate of 7.4 pounds and 37 pounds perhour' respectively so as to produce a solution of titanium trichlorideand dichloride in sodium chloride. The initial reduction was carried outat a temperature of about 900 C. with agitation of the bath. Theintroduction of titanium tetrachloride was then stopped and liquidsodium was fed in a fine stream to the surface of the salt bath at 'arate of 2 pounds of sodium per square foot of salt bath surface perhour. This feed was continued for 6 /2 hours. During this time, the bathwas allowed to remain essentially quiescent although some slight thermalcurrents may have been present. The chargewas; allowed to cool and theresultant product was-leached by means of acidified water. The leachedproduct had a crust of sintered titanium fines at the top which wasthicker under the point of sodium addition. This crust was adhered toand supported by the reactor walls and also the agitator shaft,thermocouple well and titanium tetrachloride feed tube within thereactor. Beneath the crust was the characteristic crystal structure oftitanium; A number of the product crystals had a length of one inch orlonger and an average thickness of inch. A representative sample of 72%of the resultant titanium crystals were arc melted in an inertatmosphere to form' buttons. These buttons had a Rockwell A hardness ofless; than 56. Of the total titanium produced, 57% hada Rockwell Ahardness of 49 or less.

Example II This run was almost identical to Example I except that noagitation of the salt bath was employed during the reduction of thetetrachloride and a serrated rotatable titanium disc was mounted abovethe bath for distributing the sodium. During the operation, the sodiumwas fed to this disc, as it rotated, to spray the sodium substantiallyuniformly over the surface of the bath. This rotatable disc is morefully described and claimed in the copending application of Hellier,Serial No. 442,525, filed July 12, 1954, now abandoned. The crust ofsintered titanium fines was thinner, substantially planar and moreuniform than in the case of Example I. It was located below the upperlevel of salt. Since less crust was formed, a larger percentage of thetotal product was in the form of unsintered, relatively large crystals.

Example III This run was almost identical to Example II except for thefact that the reactor was maintained at temperature (i. e., 900 C.) for6 hours after cessation of the sodium feed. This holding period providedfor substantially complete reduction of all of the dissolved titaniumchloride in the salt bath. The product from this run was very similar tothat of Example 11..

While several specific examples have been given above, numerousalternative methods may be employed without departing from the spirit ofthe invention. The temperature of the reaction mass may be varied widelyfrom slightly above the melting point of the salt to temperatures on theorder of 1000 C. and above. Numerous reducing agents other than thesodium may be employed. For example, potassium, calcium, magnesium,lithium and various combinations of these elements may be utilized. Theexpression alkaline earth metals used in the claims is intended toinclude magnesium. From the standpoint of cheapness, sodium or magnesiumis preferred. Other halides of titanium may be utilized although, fromthe standpoint of cost, ease of handling, etc., the tetrachloride ismost preferred.

The process, as illustrated in any of the examples, may be practicedwith continuous or intermittent feed of titanium chloride, either assuch or dissolved in fused salt, this feed being to a portion of thebath below the crust. In such case, an intermittent or continuousoverflow of fused salt will normally be provided at a point in thereactor where the fused salt is relatively low in titanium chloride.While agitation of the bath should be minimized, particularly While thecrust is forming, some circulation of the bath below the crust may beprovided, particularly at later stages of the process, to facilitatecomplete reduction of the titanium chlorides.

Additionally, the reactor can be fed with lower halides of titanium,such as titanium trichloride, manufactured from, titanium-bearingmaterials in the manner shown in. the: copending applications ofSingleton, Serial No. 304,388, filed August 14, 1952, now U. S. PatentNo. 2,770,541, and Singleton, Serial No. 315,461, filed October 1.8,.1952. Equally, titanium trichloride can be made by the techniquedescribed by Sherfey et al., Journal of Bureau of Standards 46, 299-300April 1951. Additionally, the dichloride of titanium can be manufacturedby numerous processes such as disproportionation of the. trichloride orpartial reduction of the trichloride or tetrachloride.

The present'invention can be equally employed for the manufacture oftitanium alloys by the coreduction of the chlorides, for example, ofvanadium, chromium, manganese, iron, nickel, cobalt, columbium,tantalum, molybdenum, tungsten or silicon. The alloy may be a binaryalloy or it may be an alloy containing 3 or 4 constituents. In themanufacture of alloys, the same general conditions of the slow reductionof the titanium halide and reducible compounds of the alloyingconstituents must be employed. Accordingly, when the expression titaniumis used in the appended claims, it is intended to include alloys oftitanium as well as pure titanium.

It shouldbe additionally pointed out that the salt mixture in which thereduction is carried out may be formed of. numerous halides which can bemixed halides, single halidesqand halides of materials other than thespecific reducing agent or agents employed in the reaction. Fromthe'standpoint of simplicity of operation and ease of control, it ispreferred, however, that the salt be the chloride of the reducing agent.Thus it is quite feasible to employ binary and ternary mixtures ofhalides having quitexlow melting points.

It should be pointed: out, in connection with a consideration of the:various salts which can be employed, that these salts should becompletely anhydrous and free of any contaminants such as carbon,nitrogen, oxygen or hydrogen. This is due to the tremendous reactivityof titanium metal at temperatures on the order of 800 C. to 900 C. andabove.

In the above specification, reference has been made particularly to thepreferred titanium chlorides, tetrachloride and dichloride. In mostinstances, the trichloride is equally useful and, as a matter of fact,it is extremely unlikely that any system having an appreciableconcentration of one of the lower chlorides of titanium will not have atleast some of the other lower chloride also present. It should. beapparent that one can also employ the corresponding di-, triandtetra-halides from the group consisting of the iodides, bromides andfluorides of titanium.

Sincev certain changes may be made in the above process withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:

I. In a process for producing titanium wherein a halide of titanium isdissolved in a fused salt bath and is reduced to titanium crystals bymeans of a metallic reducing agent selected from the class consisting ofthe alkali metals and the alkaline earth metals, the molten saltcomprising a halide selected from the group consisting of the alkalimetal halides and the alkaline earth metal halides, the improvementwhich comprises adding said reducing agent to the surface of the fusedsalt bath to initially form a titanium crust on said bath, andthereafter feeding said reducing agent to the upper surface of a layerof fused salt above the crust, the layer of fused salt above the crustbeing essentially free of dissolved titanium halide and the amount ofsaid reducing agent fed being sufficient to reduce substantially all ofthe contained titanium halide to titanium metal, and maintaining saidfused salt molten until substantially all of the contained titaniumhalide is reduced.

2. In a process for manufacturing titanium wherein a solution of a lowerchloride of titanium in a molten salt is reduced to metallic titanium bymeans of a liquid metal reducing agent, the reducing agent beingselected from the class consisting of the alkali metals and thealkaline'earth metals, the improvement which comprises uniformlydistributing the reducing agent across the surface of the molten salt toform an initial crust of sintered titanium particles on the surface ofthe salt, feeding more reducing agent to the upper surface of the moltensalt bath, and supporting the titanium crust adjacent the surface of thesalt bath during reduction of further. titanium chloride within the saltbath, the layer of fused salt above the crust being essentially free ofdissolved titanium chloride. 3. In a process for manufacturing titaniumwherein a solution of a lower chloride of titanium in a molten salt isreduced to metallic titanium by means of a liquid metal reducing agent,the reducing agent being selected'from the class consisting of thealkali metals and the alkalineearth metals, the improvement whichcomprises uniformly distributing the reducing agent across the surfaceof the molten salt to form an initial crust of sintered titanium'particles on the surface of the salt, feeding more reducing agent to theupper surface of the molten salt bath, and

supporting the titanium crust at and intermediate its edges adjacent thesurface of the salt bath during reduction of further titanium chloridewithin the salt bath, the layer of fused saltabove the crust beingessentially free of dissolved titanium chloride.

4. In a process for manufacturing titanium wherein a solution of a lowerchloride of titanium in a molten salt is reduced to metallic titanium bymeans of a liquid metal reducing agent, the reducing agent beingselected from the class consisting of the alkali metals and the alkalineearth metals, the improvement which comprises spraying said reducingagent onto the surface of the molten salt to form an initial crust ofsintered titanium particles onthe surface of the salt, and feeding morereducing agent to the molten salt adjacent the crust, the layer of fusedsalt above the crust being essentially free of dissolved titaniumchloride.

5. In a process for producing titanium wherein a chloride of titanium isdissolved in a fused salt bath and is reduced to titanium crystals bymeans of a metallic reducing agent, the reducing agent being selectedfrom the class consisting of the alkali metals and the alkaline earthmetals, the improvement which comprises providing on the surface of thefused salt bath a layer of salt which is substantially free of titaniumchlorides, and thereafter feeding to the top of saidtitanium-chloride-free salt layer sufiicient reducing agent to reducesubstantially all of the contained titanium chloride to titanium metal,and maintaining said fused salt molten until substantially all of thecontained titanium chloride is reduced.

6. In a process for producing titanium wherein a lower chloride oftitanium is dissolved in a fused salt bath and is reduced to titaniumcrystals by means of a metallic reducing agent, the reducing agent beingselected from the class consisting of the alkali metals and the alkalineearth metals, the improvement which comprises adding molten reducingagent to the surface of the fused. salt bath to.

initially form a titanium crust on said bath, and thereafter feedingsaid reducing agent to the upper surface of a layer of fused salt abovethe crust, the layer of fused salt above the crust being essentiallyfree of dissolved titanium chloride and the amount of reducing agent fedbeing sulficient to reduce substantially all of the con-' tainedtitaniumchloride to titanium metal, and maintaining said fused salt molten untilsubstantially all of the contained titanium chloride is reduced.

7. In a process for producing titanium wherein a halide of titanium isdissolved in a fused salt bath and is re duced to titanium crystals bymeans of a metallic reducing agent selected from the class consisting ofthe alkali" metals and the alkaline earth metals, the molten saltcomprising a halide selected from the group consisting of the alkalimetal halides and the alkaline earth metal halides, the improvementwhich comprises providing on the surface of the fused salt bath a layerof salt which is substantially free of titanium halides, and thereafterfeedingcomprising a halide selected from the class consisting of thealkali metal halides and the alkaline earth metal halides, theimprovement of which comprises maintaining between the supply ofreducing agent anda; major portion of the salt bath containing thedissolved titanium halide a zone comprising said fused salt which issubstantially free of titanium halide, the reducing agent beingintroduced into and passed through the shielding layer to react with thetitanium halide.

9. A process for manufacturing titanium wherein a titanium lowerchloride is dissolved in a bath of a fused salt and is reduced totitanium crystals by supplying a metallic reducing agent to the bath,the reducing agent comprising a metal selected from the class consistingof the alkali metals and the alkaline earth metals and. the fused saltcomprising a halide selected from. the class consisting of the alkalimetal halides and thealkaline earth metal halides, theimprovement ofwhich comprises maintaining between the supply of reducing agent and theportion of the salt bath containing the dissolved titanium lowerchloride a shielding layer of fused salt which is substantially free oftitanium lower chloride, the reducing agent being introduced into andpassed through the shielding layer to react with the titanium chloride.

References Cited in the file of this patent UNITED STATES PATENTS

